Influence of the time constant of DC component on interrupting duty of GCB

The time constant of the DC component of fault currents in Japanese power systems has gradually been increased due to the concentration of power sources and utilization of large capacity transmission lines. Large time constants of the DC component are proposed in the new draft of future IEC 60056 and the latest Japanese standard (JEC-2300-1998). From the point of view of reliability in the system, it is important to investigate the influence of the time constant of DC component on interrupting duty of GCB. The authors performed interrupting tests with asymmetrical current on 550 kV 63 kA GCB by the equivalent test method. The procedure of the equivalent test method is as follows: decision of the arcing time in single-phase short-circuit test considering maximum arc energy in three-phase terminal fault; waveform simulation of the interrupting current at the last major loop; and evaluation of dielectric recovery characteristics using 2-part method.